Process for the chemical nickel-plating of nonmetallic articles

ABSTRACT

Chemical nickel-plating of nonmetallic articles, which are (a) cleaned by mechanical and/or chemical treatment, (b) activated later by means of an aqueous palladium slat solution, of which the palladium salt is reduced to palladium, and (c) immersed in a nickel-plating bath, which is preheated to a temperature between about 30* and 70* C., contains nickel and hypophosphite ions, one or more buffer substances, and is maintained at a pH-value between 3 and 9, comprising carrying out the nickel-plating with the use of a nickel-plating bath containing one or more phosphonic acid compounds corresponding to either the following general formula   OR THE GENERAL FORMULA

United States Patent [72] Inventors Joachim Kandler Lechenich; Gerhard Mietens, Walberberg; Michael Ahlgrim, Bliesheim, all of Germany [21] App]. No. 771,643 [22] Filed Oct. 29, 1968 [45] Patented Nov. 2, 1971 [73] Assignee Knapsack Aktiengesellschalt Knapsack bei Cologne, Germany [32] Priorities Dec. 9, 1967 [33] Germany [31] P 16 21 275.2;

Dec. 9, 1967, Germany, No. P 16 21 276.3; Jan. 17, 1968, Germany, No. P 19 69 113.0

[54] PROCESS FOR THE CHEMICAL NICKEL- PLATING 0F NONMETALLIC ARTICLES 2 Claims, No Drawings [52] US. Cl 117/47 R, 117/130 E,117/160,106/1, 252/351, 260/502.5 [51] Int. Cl B4441 1/092, C23c 3/02 [50] Field of Search 117/130 E, 47 R, 160; 252/351; 260/502.5; 106/1 [56] References Cited UNlTED STATES PATENTS 2,599,807 6/1952 Bernsworth 260/5025 3,234,124 2/1966 210/38 3,468,935 9/1969 252/351 X 3,484,282 12/1969 Gabler 106/1 X Primary Examiner-Alfred L. Leavitt Assistant Examiner-Janyce A. Bell Attorney-Connolly and Hutz ABSTRACT: Chemical nickel-plating of nonmetallic articles, which are (a) cleaned by mechanical and/or chemical treatment, (b) activated later by means of an aqueous palladium slat solution, of which the palladium salt is reduced to palladium, and (c) immersed in a nickel-plating bath, which is preheated to a temperature between about 30 and 70 C., contains nickel and hypophosphite ions, one or more buffer substances, and is maintained at a pl-l-value between 3 and 9, comprising carrying out the nickel-plating with the use of a nickel-plating bath containing one or more phosphonic acid compounds corresponding to either the following general formula or the general formula PROCESS FOR THE CHEMICAL NICKEL-PLATING OF NONMETALLIC ARTICLE? A process for the chemical nickel-plating of articles which have a catalytic" surface, has been described in German Pat. 1,077,940. The process substantially comprises treating the articles by means of a bath containing nickel and hypophosphite ions. The term catalytic" as used in this context is intended to mean that at least the material forming the article surface is capable of catalyzing the oxido-reduction between the nickel ions and the hypophosphite ions, that causes the nickel to precipitate on the catalytic surface.

To ensure correct precipitation of nickel, the bath is primarily required to contain the reactants in specific proportions, i.e. the bath is required to contain:

Ni and l-l,PO ions in a quantitative ratio between 0.25 and 1.60to contain H,P0, in an absolute concentration between 0.15 and 1.20 mols/liter; and to have a pl-l-value between 4.3 and 6,8, which is maintained by means of a buffer present therein and by the addition of alkali during the reaction.

Furthermore, to be active and useful for some prolonged time, the bath is required to contain so-called activating agents formed of saturated, aliphatic dicarboxylic acids having three to six carbon atoms, such as succinic acid. The reaction is finally required to be carried out at a temperature between 95 and 99 C.

As the applicability of the above process is limited to the chemical nickel-plating of articles having a catalytic" surface, it cannot as it stands be used generally for metallizing nonmetallic articles, as proposed in the present invention.

It has already been reported that the surface of nonmetallic articles can be treated to receive, for example, a metallic nickel-plating. To this end, the article is firstcleaned to activate its surface which is roughened thereafter, and pretreated by means of a palladium salt solution. The palladium chloride is reduced to palladium and the article so activated is immersed thereafter in a bath containing nickel and hypophosphite ions. Reference is made to the process described in German published Specification 1,182,015, which enables the surfaces, for example, of plastics, rubber, glass, wooden or ceramic material to be metallized. The palladium chloride solution suitable for surface activation preferably has concentration of 35 milli-grarns per liter. When hypophosphite is the reducing agent, it is advantageous to dissolve it in the metallization bath in a concentration of 0.225 mol/liter.

ln accordance with the process of German Pat. 1,198,643, the palladium-activated article should preferably be nickelplated first with the use of a dilute preliminary bath containing Ni and H,PO, in a molar ratio of about 0.25 and, after formation of a continuous nickel plating, the article should be treated further by means of a bath customary in nickel-plating. The preliminary nickel-plating bath is said to avoid the induction period usually needed for the nickel to precipitate on the dispersed palladium particles as the growth-promoting nuclei, and to improve the bond strength of the nickel plating. The preliminary nickel-plating bath can contain, for example, the following components:

NaH,FO, 0.225 mol/liter ",BC, 0.02 mol/liter I-1.330, 0.09 mol/liter The preliminary bath used in carrying out the nickel-plating should have a pH-value between 5.5 and 7 and a temperature between 10 and 30 C. To increase the nickel-plating velocity, the bath can be used in combination with an ordinatherewith, in the suggested temperature range of 10 to 30 C., so that a layer not thicker than 1 to 1.2 p. is produced per hour. 1n the event that the temperature is increased to a value higher than 30 C., the preliminary nickel-plating bath is found to undergo spontaneous self-decomposition with the resultant formation of colloidal nickel, and to become useless.

The process of German Pat. 1,077,940 mentioned above'is not applicable to thedirect nickel-plating of nonmetallic articles, for example plastics. The reasons for this are that thermoplastics, for example, undergo plastic deformation at a temperature of -99 C. needed for the nickel-plating bath, and that the precipitated layer of nickel would be foundto have a poor bond strength.

The disadvantages associated with the earlier processes are obviated in the precess described in U.S. Pat. No. 3,506,802.

This process for the chemical nickel-plating of nonmetallic articles which are (a) cleaned by mechanicaland/or chemical treatment, (b) activated thereafter by means of'an aqueous palladium salt solution, of which the palladium salt is reduced to palladium, and (c) immersed in a preheated nickel-plating bath,which contains nickel and hypophosphite ions and a buffer substance and is maintained at a pl-l-valuebetween '3 and 9, comprises nickel-plating the said articles using a nickelplating bath containing nitrilotrismethylene-phosphonic acid as an additional component and heated to a temperature between 30 and 70 C.

Reliable and optimum precipitationof nickel is ensured when the bath used for carrying out the nickel-plating contains the hypophosphite ions in a concentration of about 0.25 to 1 mol per liter, which is convenient. It is also advantageous to provide for a molar ration of Nl -lOl1S to H,PO='-ions of about 0.2 to 1.6 in the bath.

in accordance with a further feature of that process, the nickel-plating bath contains Ni"-ions and nitrilo-trismethylene-phosphonic acid in a molar ratio between 0.7 and 2.0.

ln carrying out the process of U.S. Pat. No. 3,506,802, it has finally been found that a bath maintained at a pl'l-value of 3 to 9, preferably 5 to 6, causes the nickel to precipitate under especially favorable conditions. A phosphate buffer containing, per liter, 0.02 to 0.1 mol, preferably 0.067 mol Na,HPO 211,0, and 0.002 to 0.1 mol, preferably 0.0067 mol Kl-LPO has proved very suitable for maintaining the above pl-l-values. In addition to buffering the solution, the phosphate buffer is found to participate in the stabilization of the bath, at the pH- values indicated above. pH-values and temperatures higher than those specified above accelerate the precipitation of nickel, but they reduce the stability of the bath and impair the bond strength of the nickel plating. ln the case of a bath having a pl-l-value higher than 7, it is possible further to increase the baths stability in conventional manner by the addition of a stabilizer, such as lead sulfide or lead acetate, which is used in a proportion of 2 milligrams per liter. In the following table there is indicated the bath temperature which should preferably be used at a given pH-value, at which the bath is found to have a good stability and the nickel plating precipitated on the surface of the articles to be metallized is found to have the necessary bond strength.

TABLE pl-l-value 4 5 6 7 8 Temperature C. 65 60 50 40 30 Under these conditions, the nickel is found to precipitate uniformly per unit of time on the surface of the article. 1n view of the fact that the nickel-plating bath having the above composition practically needs no induction period for the nickel to commence precipitation, it is clear that the articles dipped in the nickel-plating bath are completely metallized after no more than 15 seconds. After 2 to 3 minutes, the precipitated nickel plating has a thickness of about 3 to 3.5 u. The nickel plating, which is really formed of a nickel-phosphorus alloy containing 5 to percent phosphorus, adheres very tenaciously to nonmetallic articles of which the surface has been activated in convenient manner, prior to the metallization. The nickel plating precipitated by the process of Pat. Application No. 651,968, can be reinforced by means of electrodeposited nickel, polishednickel and polished chromium coatings, or may receive a ductile copper coating as a first reinforcing coating. The pretreatment of the article to be plated in an attempt to activate its surface can be carried out, for example, in the manner set forth in German Pat. 1,182,015.

The process of U.S. Pat. No. 3,506,802 can be used for the nickel-plating of nonmetallic substances or articles, such as glass, Bakelite polypropylene or plastics obtained by the graftpolymerization of acrylonitrile, butadiene and styrene.

As compared with conventional baths used for nickel-plating, the bath produced by the process of U.S. Pat. No. 3,506,802 offers the following advantages:

1. The presence of nitrilo-trismethylene phosphonic acid means high precipitation velocity for the nickel at temperatures of the nickel-plating bath between 30 and 70 C., so that nonmetallic articles pretreated in convenient fashion, can be metallized more rapidly than heretofore.

2. The bath is very stable and therefore easy to manipulate.

3. Practically no induction period is needed for the nickel to commence precipitation.

4. No preliminary bath is needed for carrying out the nickelplating.

The bath used in carrying out the above nickel-plating process can be regenerated in customary manner by means of hypophosphite and nickel ions, for example by the process disclosed in German Pat. 1,107,045. The regeneration is very easy to achieve as there is no need for cooling the bath liquid prior to the addition of the regenerating agent.

It has now unexpectedly been found that a nickel-plating bath, wherein the nitrilotrismethylene phosphonic acid component is replaced by one or more of the phosphonic acid compounds suggested to be used in accordance with the present invention produces, under otherwise identical process conditions, the same advantageous effects as those which are produced by the process described in U.S. Pat. No. 3,506,802 and which so favorably distinguish this process over the prior art processes. The point of distinction of the present invention over the process described in U.S. Pat. No. 3,506,802 thus resides in the substitution of one or more of the suggested phosphonic acid compounds for the nitrilo-trismethylene phosphonic acid.

The present process for the chemical nickel-plating of nonmetallic articles, carried out in accordance with U.S. Pat. No. 3,506,802, wherein the articles are (a) cleaned by mechanical and/or chemical treatment, (b) activated later by means of an aqueous palladium salt solution, of which the palladium salt is reduced to palladium, and (c) immersed in a nickel-plating bath, which is preheated to a temperature between about 30 and 70 G, contains nickel and hypophosphite ions, one or more buffer substances and phosphonic acid compounds, and is maintained at a pH-value between 3 and 9, comprises more especially carrying out the nickel-plating with the use of a nickel-plating bath containing one or more phosphonic acid compounds corresponding to either the following general form alllL- A Rg-CXY in which X and Y stand for hydrogen atom or an alkyl group having one to six carbon atoms, R, and R, stand for a JO H;- group or a -C0Ol-l-group or stand for a group corresponding to the following formula (ll) cxy n;

CHN

CXY-R; (II) and R stands for a -PO l-l -group or a -COOH-group, whereby it is imperative for the phosphonic acid compound to contain at least one -PO H -group; or corresponding to the general formula III) A W P 03H: (Jill in which 2 stands for a hydrogen atom, an -OH-group or -HN,- group and R stands for a hydrogen atom or an alkyl group having one to six carbon atoms or stands for a group corresponding to the following formula (IV) CXY-Rl CXY-Rs in which formula (IV) X and Y stand for a hydrogen atom or an alkyl group having 1 to 6 carbon atoms and R and R, stand for a -PO H -group, a -COOl-l-group or a -COOH-group and a -PO H -group.

In the process of the present invention, the Ni-ions and the phosphonic acid compound are preferably used in a molar ratio between about 0.7 and 2.0.

The phosphonic acid compounds suitable for use in the present process include, for example: ethylene-diamineteu'amethylene phosphonic acid; nitrilo-monoacetic aciddimethylene phosphonic acid; ethylene-diamine-diacetic aciddimethylene phosphonic acid; l-hydroxyethanel diphosphonic acid; ethylene-l-aminodimethylene phosphonic acid-2-hydroxy-2,Z-diphosphonic acid, which can be used.

singly o in con bination. F u rther jnt er e s ting compounds include: ethylene-l-amino-diacetic acid-2,2-diphosphonic acid; ethylene-l-amino-diacetic acid-2-amino-2,2-diphosphonic acid. The amino-diacetic acid-substituent can be replaced in each particular case by an amino-group, which has an acetic acid radical as well as a methylene phosphonic acid gdical linkgd the gtg 'mckel-plating bath containing one or more of the above phosphonic acid compounds enables the same advantageous effects as those produced by the process described in U.S. Pat. No. 3,506,802 to be obtained, as already mentioned above, i.e. the following advantages: 1. The presence of the phosphonic acid compound or compounds means high precipitation velocity for the nickel at temperatures of the nickel-plating bath between 30and 70 C., so that nonmetallic articles pretreated in convenient fashion, can be metallized more rapidly than heretofore. 2. The bath is very stable and therefore easy to manipulate. 3. Practically no induction period is needed for the nickel to commence precipitation. 4. .No preliminary bath is needed for carrying out the nickel-plating.

The following examples further illustrate the process of the present invention.

EXAMPLE 1 Shaped plastics obtained by graft polymerization of acrylonitrile, butadiene and styrene were chemically nickelplated. Prior to being nickel-plated, their surfaces had been cleaned and degreased by means of an aqueous solution of a commercial surface-active substance, chemically roughened later at 60 C. for 15 minutes with the use of chromosulfuric acid, and ultimately sensitized with an aqueous tin chloride solution in hydrochloric acid. Thereafter, the surfaces of the shapes had been activated by means of a PdCl solution in hydrochloric acid.

Following this conventional pretreatment, the shaped plastics were nickel-plated by means of a nickel-plating bath prepared in accordance with the present invention, the bath containing:

NiSO '7H,O 0.1 l moi/liter NaH,PO,.H,O 0.28 mol/liter ethylene-diamine-tetrameLhylene-phos 0.1 l mol/liter phonic acid Na,HPO ZH,O 0.067 moi/liter KH,PO, 0 0067 mol/liter The bath was adjusted by means of sodium hydroxide solution to have a pH-value of 6.0 and heated to 50 C. The shapes clamped to insulated holders, were dipped in the slightly agitated bath liquid. A continuous, well-adhering nickelplating was found to have precipitated on the shapes within a period of seconds, which, after a further 3 minutes, was found to be capable of being electro-plated.

EXAMPLE 2 Modified polypropylene shapes were pretreated in a manner analogous to that described in example 1. The nickelplating was carried out using a nickel-plating bath containing:

NiSO,-7H,0 0.11 moi/liter NaH,PO,-H,O 0.28 mol/liter nitrilo-monoacetic acid-dimethylene phosphonic acid 0.13 mol/liter Na,HPO,2H,O 0.067 mol/liter KH,P0, 0.0067 mol/liter bath temperature 60 C.

pH-value 5.0

A continuous, well-adhering nickel plating was found to have precipitated on the shapes within a period of 20 seconds, which, after a further 3 minutes, was found to be capable of being electro-plated.

EXAMPLE 3 Shaped plastics obtained by the graft polymerization of acrylonitrile, butadiene and styrene were pretreated in the manner described in example 1.

Following the pretreatment, the shaped plastics were nickel-plated by means of a nickel-plating bath prepared in accordance with the present invention, the bath containing:

NiSO,'7H,O 0.13 mollliter NaH,PO,-H,O 0.40 moi/liter l-hydroxyethane-l ,l -di hosphonic acid 0.15 mollliter Na,H PO,-2H,0 0.067 mollliter KH,PO, 0.0067 mol/liter The bath was adjusted by means of sodium hdyroxide solution to have a pH-value of 6.5 and heated to 45 C. The shapes clamped to insulated holders, were dipped in the slightly agitated bath liquid. A continuous, well-adhering nickel plating was found to have precipitated on the shapes within a period of 20 seconds, which, after a further 3 minutes, was found to be capable of being electroplated.

EXAMPLE 4 Modified polypropylene shapes were pretreated in a manner analogous to that described in example 3. The shapes were roughened at C. within a period of 20 minutes by means of chromosulfuric acid. The nickel plating was carried out using a nickel-plating bath containing:

NiSO,-7H,O 0.085 mollliter NaH,PO,-H,O 0.25 mol/litcr ethylene-l-aminodimethylenc-phosphonic 0.09 moI/Iiter acid-2-hydroxy-2,2-diphosphonic acid Na," P0, 2H,O 0.067 mol/liter KH,PO 0.0067 mol/liter temperature 55 C.

H-value 5 .5

A continuous, well-adhering nickel plating was found to have precipitated on the shapes within a period of 20 seconds, which, after a further 3 minutes, was found to be capable of being electro-plated.

We claim:

1. In the process for the chemical nickel plating of nonmetallic articles, which are (a) cleaned, (b) activated later by means of on aqueous palladium salt solution, of which the palladium salt is reduced to palladium, and (c) immersed in a nickel-plating bath, which is preheated to a temperature between about 30 and 70 G, contains nickel and hypophosphite ions, one or more buffer substances and phosphonic acid compounds, and is maintained at a pH-value between 3 and 9, 

2. The process of claim 1 wherein the molar ratio of Ni -ions to phosphonic acid compound is between about 0.7 and 2.0. 